1. Field of the Invention
The present invention relates to a digital broadcast transmission system, and more particularly, to a digital broadcast transmission system offering improved receptability at a receiving end, and a signal processing method thereof.
2. Description of the Related Art
FIG. 1 is a schematic block diagram of an 8-VSB transmission system. The 8-VSB transmission system comprises an error correction encoding unit 110, a synchronous signal inserting unit 120, a pilot inserting unit 130, a pulse shaping filter 140 and a radio frequency (RF) unit 150.
The error correction encoding unit 110 comprises a randomizer 111, a Reed-Solomon (RS) encoder 113, an interleaver 115 and a Trellis encoder 117.
The randomizer 111 randomizes an incoming sequence of MPEG2-TS data packets, and the RS encoder 113 adds predetermined bytes of RS parities for error correction of data packets. The interleaver 115 carries out convolution interleaving, and the Trellis encoder 117 carries out Trellis encoding at a 2/3 ratio.
The synchronous signal inserting unit 120 inserts segment sync and field sync with respect to the data packets which are error-correction encoded.
The pilot inserting unit 130 generates one pilot signal by adding a predetermined DC value to 8-level symbol data.
The pulse shaping filter 140 carries out pulse shaping with respect to a VSB signal containing a pilot signal therein, by the filter which has a predetermined roll-off factor.
The RF unit 150 up-converts data into RF channel domain, and transmits the converted data via antenna.
FIG. 2 is a frequency spectrum of an 8-VSB signal which is pulsed-shaped at the pulse shaping filter 150 of the 8-VSB transmission system of FIG. 1. As shown, the 6 MHz channel bandwidth consists of at least 5.38 MHz of bandwidth for the transmission of the 8-VSB signal, and excess bandwidths of 6 KHz (0.31 KHz×2) at both sidebands of the 5.38 MHz bandwidth, according to the roll-off factor of the pulse shaping filter. There is one pilot signal in the low frequency band. The pilot signal as inserted is used in the receiving system in the processes such as carrier frequency recovery.
The conventional 8-VSB transmission system as described above, however, has a problem in decoding when the pilot signal disappears due to poor channel environments.